A circuit arrangement of this type is particularly required in digitally operating devices in order to deliver a monitoring signal which is used as a switch-off criteria for such devices which may be controlled only through defined logic conditions. If, for example, the operating voltage varies in data processing equipment, logic conditions which are defined below a pregiven nominal operating voltage cannot be maintained in the individual operating units. Output equipment, which are controlled by such a disturbed logic condition, can generate undefined outputs and thus give false data. It is, for example, possible to operate in an uncontrolled manner a recording instrument or also a core storage device whereby the stored information is possibly destroyed.
If digital operating units of data processing equipment, which units interact with one another, are fed through several supply voltages, it is possible, aside from the described power-supply voltage variations, during switching off or switching on of the current supply net for the individual supply voltages to drop off with different time constants or to reach their nominal value. Thus, the case may occur that an operating unit receives its full supply voltage, however, is controlled by a different operating unit with an undefined variable digital input.
Thus, it is necessary to produce as quickly as possible a characterizing signal for operations of the described type which cause errors and to thus characterize the logic condition which is to be monitored, thus, for example, the voltage condition of a current supply device at a pregiven deviation. The signal is to deliver a fixed pregiven logic condition which is independent from an operating voltage and reliably assures the switching off of faultily operating or faultily controlled operating units.
Within data processing equipment such a characterizing signal is produced on a special signal line. Same could, for example, consist of a chain circuit of switches which are each associated with an operating unit or current supply unit and are closed when the respective orderly function exists. When a faulty mode of operation occurs in one of the monitored devices, the switch which is associated with it would be opened and the entire chain circuit would become currentless so that therewith simultaneously a criteria which characterizes the faulty condition of a device would be produced. However, the use of a chain circuit has the disadvantage that a change of a unit, for example, the removal of or the additional insertion of a device which is to be monitored, always results in electrical and structural changes of the described chain circuit.
The purpose of the invention is to produce a circuit arrangement for producing a defined logic condition, which is fed alone through the logic system which must be monitored and thus operates without any special or separate operating voltage. The circuit arrangement furthermore permits a simple signal output which requires no changes of the electrical or structural type when changes occur in the entire monitored unit.
A circuit arrangement of the above-named type is constructed inventively to attain this purpose in such a manner that the condition which is to be monitored is connected to the control path of a switch device which is conductively controlled therethrough, the switch path of the switch device being connected into a control circuit of a semiconductor arrangement having thyristor characteristics, which semiconductor arrangement emits the defined condition at its anode-cathode path, and that the anode point of this semiconductor arrangement is connected to its control electrode through an ohmic resistor.
This circuit arrangment operates without any operating voltage and can be connected through only two different logic conditions which appear at its control input and if the control current does not exist can carry comparably strong currents. It then produces the criteria U = 0 on a signal line. Thus, an arrangement is realized which, independent from a special operating voltage and its variations, is switched alone by the signal controlling it and has thereby a switching characteristic of an inactive contact. The arrangement can therefore be operated together with other similarly operating circuits connected in parallel on one signal line without influencing same through the switching characteristics of the other circuits. Contrary to a pure thyristor circuit, the circuit arrangement of the invention can also be quenched at its control input, for which only the control current must be switched on. A particular advantage of this circuit arrangement consists in that the voltage which is required at its anode-cathode path for carrying out a switching operation can be lowered to values which are paractically equal to the saturation voltage and which drops off from it in the conductive condition. This is due to the fact that through an ohmic resistor, a current flow is possible to the semiconductor element which it does not by-pass and which must be only large enough to start a conducting operation and that this semiconductor element has a current amplification factor which is greater than 1.
A circuit arrangement according to the invention can be associated with a unit which must be monitored with respect to its operation. Thus, the unit may be part of a current supply device or other units of data processing equipment. Several existing conitoned circuits of this type can then be connected in parallel with one another to a common signal line or common main, to which they deliver the defined logic condition which they each produce and the common line can be connected to a control device which effects the switching off of sensitive operating units to undefined input values.
According to a further construction embodied within the scope of the invention, the ohmic resistor is preferably dimensioned corresponding to the voltage which, in conducting condition of the semiconductor arrangement, exists across it and the current which flows during a blocked or nonconductive anode-cathode path of the circuit arrangement flows through the control path of the semiconductor element which is not by-passed by this resistor. In the case of such a dimensioned ohmic resistor, the conducting voltage of the semiconductor arrangement is practically equal to the saturation voltage which in the conductive condition exists across it. The current which is needed for conduction lies for both semiconductor arrangements in the order of magnitude of some microamperes so that a common line which is connected to the anode-cathode path is loaded at a minimum.